Measurement procedures for DRS with beamforming

ABSTRACT

Systems and methods relating to transmission and use of Discovery Reference Signal (DRS) signals are disclosed in herein. In some embodiments, a method of operation of a Transmission Point (TP) in a cellular communications network comprises transmitting, from the TP, a same one or more DRS signals using at least two different transmit beams in at least two different time resources. Each transmit beam is characterized by a direction in which it is transmitted. In this manner, the TP is enabled to reuse DRS resources, which in turn enables transmission of DRS signals on a larger number of transmit beams and, correspondingly, adaptation of measurement procedures at wireless devices to obtain measurements on those transmit beams.

RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 16/586,362, filed Feb. 10, 2020, granted as U.S.Pat. No. 10,917,142 on Feb. 9, 2021, which is a divisional applicationfrom U.S. patent application Ser. No. 15/573,206, filed Nov. 10, 2017,granted as U.S. Pat. No. 10,469,138 on Nov. 5, 2019, which is a 35U.S.C. § 371 national phase filing of International Application No.PCT/162016/052709, filed May 11, 2016, which claims the benefit of U.S.Provisional Patent Application No. 62/161,788, filed May 14, 2015, thedisclosures of which are hereby incorporated herein by reference intheir entireties.

TECHNICAL FIELD

This disclosure pertains to measurement procedures for discovery signalswith beamforming.

BACKGROUND Long Term Evolution (LTE) Frame Structure and ReferenceSignals

Third Generation Partnership Project (3GPP) LTE technology is a mobilebroadband wireless communication technology in which transmissions frombase stations (referred to as enhanced or evolved Node Bs (eNBs)) towireless devices (e.g., mobile stations) (referred to as User Equipmentdevices (UEs)) are sent using Orthogonal Frequency Division Multiplexing(OFDM). OFDM splits the signal into multiple parallel sub-carriers infrequency. As illustrated in FIG. 1 , the basic unit of transmission inLTE is a Resource Block (RB), which in its most common configurationconsists of 12 subcarriers and 7 OFDM symbols (one slot). A unit of 1subcarrier and 1 OFDM symbol is referred to as a Resource Element (RE).Thus, an RB consists of 84 REs. An LTE radio subframe is composed of twoslots in time and multiple RBs in frequency with the number of RBsdetermining the bandwidth of the system. Furthermore, the two RBs in asubframe that are adjacent in time are denoted as an RB pair. FIG. 2illustrates an RB pair in a downlink subframe. Currently, LTE supportsstandard bandwidth sizes of 6, 15, 25, 50, 75, and 100 RB pairs.

In the time domain, LTE downlink transmissions are organized into radioframes of 10 milliseconds (ms), each radio frame consisting of tenequally-sized subframes of length T_(subframe)=1 ms.

Discovery Signals for Small Cells

With the densification of small cells (cells with lower transmissionpower and thus smaller coverage) and potentially increased number ofcarriers in small cell scenarios, Discovery Reference Signal (DRS)features have been introduced in 3GPP LTE Release 12 (Rel-12). InRel-12, a DRS occasion has been defined as a duration within which DRSsignals are transmitted by a cell. The DRS signals included in the DRSoccasion on a cell are shown in FIG. 3 . In particular, FIG. 3illustrates REs used by DRS signals in a Physical RB (PRB) pair for twodifferent cells (e.g., transmitted by two different Transmission Points(TPs)). As shown, the DRS signals include a Primary SynchronizationSignal (PSS), a Secondary Synchronization Signal (SSS), a CommonReference Signal (CRS), and, if configured, a Channel State InformationReference Signal (CSI-RS). With respect to CSI-RS, FIG. 3 illustratesboth REs used for CSI-RS belonging to the DRS occasion as well as REspotentially used for CSI-RS belonging to a DRS occasion. While the DRSsignals enable small cell on/off, they can also be utilized when smallcell on/off is not being used in a cell and also in non-small cells(with arbitrary transmission power).

The DRS signals in a DRS occasion are comprised of the PSS, the SSS, theCRS, and, when configured, the CSI-RS. The PSS and the SSS are used forcoarse synchronization, when needed, and for cell identification. TheCRS is used for fine time and frequency estimation and tracking and mayalso be used for cell validation, i.e., to confirm the cell Identity(ID) detected from the PSS and the SSS. The CSI-RS is another signalthat can be used in dense deployments for cell or TP identification.FIG. 3 shows the presence of these signals in a DRS occasion of lengthequal to two subframes and also shows the transmission of the signalsover two different cells or TPs.

The DRS occasion corresponding to transmissions from a particular cellmay range in duration from one to five subframes for Frequency DivisionDuplexing (FDD) and two to five subframes for Time Division Duplexing(TDD). The subframe in which the SSS occurs marks the starting subframeof the DRS occasion. This subframe is either subframe 0 or subframe 5 inboth FDD and TDD. In TDD, the PSS appears in subframe 1 and subframe 6while in FDD the PSS appears in the same subframe as the SSS. The CRSsare transmitted in all downlink subframes and Downlink Part of theSpecial Subframe (DwPTS) regions of special subframes.

The CSI-RS may be transmitted in any of the downlink subframes, but withany restrictions associated with each subframe. For the purposes of theDRS signal, only a single port (port 15) of CSI-RS is transmitted. Thereare up to twenty possible RE configurations within a subframe, althoughthe number of configurations is restricted to 5 in subframe 0 (toaccount for transmission of the Physical Broadcast Channel (PBCH) whichuses many of the same REs in the six PRBs centered around the carrierfrequency) and to 16 in subframe 5. In a DRS occasion transmitted from acell, a CSI-RS intended to represent a single measureable entity,loosely referred to as a TP, can occur in any RE configuration in any ofthe downlink subframes that are part of the DRS occasion. Thus,considering that the DRS occasion may be up to 5 subframes long in anFDD frame structure, the largest possible number of CSI-RS REconfigurations is 96. This occurs when the DRS occasion starts withsubframe 5 (a DRS occasion starting in subframe 0 would support fewerCSI-RS RE configurations) and consists of 16 configurations in subframe5 and 20 in each of the four following subframes.

It is possible for a cell or TP to transmit CSI-RS in some CSI-RS REconfigurations and transmit nothing in other CSI-RS RE configurations.The CSI-RE configurations where some signals are transmitted are thenindicated to the UE as Non-Zero Power (NZP) CSI-RS RE configurations,while the CSI-RS configurations where nothing is transmitted areindicated as Zero Power (ZP) CSI-RS RE configurations. Using the NZP andZP CSI-RS RE configurations, CSI-RS from two different cells or TPs canbe effectively made orthogonal as shown in FIG. 3 .

In each CSI-RS RE configuration, the symbols transmitted in the REs maybe scrambled with a sequence dependent on a Virtual or Configurable CellID (VCID) which can take the same set of values as the Release 8 cellID, i.e., up to 504 values. Although this creates the possibility of avery large number of CSI-RS possibilities, two CSI-RSs being transmittedwith different scrambling codes over the same REs are not orthogonal.Hence, it is less robust to separate different CSI-RS transmissionsusing only scrambling codes as compared to using different REconfigurations.

Radio Resource Management (RRM) Measurements with DRS

A description of how RRM measurements are performed with DRS signals isnow provided. The DRS signals should be useable by the UE for performingcell identification, Reference Signal Received Power (RSRP), andReference Signal Received Quality (RSRQ) measurements. The RSRPmeasurement definition based on DRS signals is the same as in priorreleases of LTE. The Received Signal Strength Indication (RSSI)measurement is defined as an average over all OFDM symbols in thedownlink parts of the measured subframes within a DRS occasion. The RSRQis then defined asDRSRQ=N×DRSRP/DRSSI,where N is the number of PRBs used in performing the measurement, DRSRPis the RSRP measurement based on the DRS signals, and DRSSI is the RSSImeasured over the DRS occasion.

In Rel-12, RSRP measurements based on the CRS and CSI-RS in the DRSoccasions and RSRQ measurements based on the CRS in the DRS occasionshave been defined. As stated earlier, DRS signals can be used in a smallcell deployment where the cells are being turned off and on or in ageneral deployment where the on/off feature is not being used. Forinstance, DRS signals could be used to make RSRP measurements ondifferent CSI-RS configurations in the DRS occasion being used within acell, which enables the detection of different TPs in a shared cell.

When measurements are made on the CSI-RS in a DRS occasion, the UErestricts its measurements to a list of candidates sent to the UE by thenetwork via Radio Resource Control (RRC) signaling. Each candidate inthis list contains a Physical Cell ID (PCI), a VCID, and a subframeoffset indicating the duration (in number of subframes) between thesubframe where the UE receives the CSI-RS and the subframe carrying theSSS. This information allows the UE to limit its search. The UEcorrelates to the received signal candidates indicated by the RRC signaland reports back any CSI-RS RSRP values that have been found to meetsome reporting criterion, e.g., exceeding a threshold value.

When a UE is being served on multiple carrier frequencies via a PrimaryCell (PCell) and one or more Secondary Cells (SCells), the UE needs toperform RRM measurements on other cells on the currently used carrierfrequencies (intra-frequency measurements) as well as on cells on othercarrier frequencies (inter-frequency measurements). Since the discoverysignals are not transmitted continuously, the UE needs to be informedabout the timing of the discovery signals so as to manage its searchcomplexity. Furthermore, when a UE is being served on as many carrierfrequencies as it is capable of supporting and inter-frequency RRMmeasurements need to be performed on a different carrier frequency thatis not currently being used, the UE is assigned a measurement gappattern. This gap pattern on a serving frequency allows the UE to retuneits receiver from that serving frequency to the other frequency on whichmeasurements are being performed. During the duration of the measurementgap, the UE cannot be scheduled by the eNB on the current servingfrequency. Knowledge of the timing of the discovery signals isespecially important when the use of such measurement gaps is needed.Beyond mitigating UE complexity, this also ensures that the UE is notunavailable for scheduling for prolonged periods of time on the currentserving frequencies (PCell or SCell).

The provision of such timing information is done via a DiscoveryMeasurement Timing Configuration (DMTC) that is signaled to the UE. TheDMTC provides a window with a duration of 6 ms occurring with a certainperiodicity and timing within which the UE may expect to receive DRSsignals. The duration of 6 ms is the same as the measurement gapduration as defined currently in LTE and allows the measurementprocedures at the UE for DRS signals to be harmonized regardless of theneed for measurement gaps. Only one DMTC is provided per carrierfrequency including the current serving frequencies. The UE can expectthat the network will transmit DRS signals so that all cells that areintended to be discoverable on a carrier frequency transmit DRS signalswithin the time window configured by the DMTCs. Furthermore, whenmeasurement gaps are needed, it is expected that the network will ensuresufficient overlap between the configured DMTCs and measurement gaps.

In order to ensure the operating efficiency of the network, it isimportant that the different sets of UEs being served by an eNB do nothave the same measurement gap pattern defined for inter-frequencymeasurements so that all UEs are not unavailable for schedulingsimultaneously on the serving carrier frequency. FIG. 4 and FIG. 5 showsome possible configurations of DMTC time windows or measurement gapsfor UEs that satisfy the above constraints. In FIG. 4 , the measurementgap or DMTC periodicity is set to be a multiple of the DRS occasionperiodicity. The UEs being served by the eNB on a serving frequency arethen partitioned into multiple non-overlapping groups. In FIG. 4 , theDRS occasion periodicity is 40 ms while the measurement gap and the DMTCis configured to occur every 80 ms. The UEs are partitioned into twogroups so that when one group of UEs is performing inter-frequencymeasurements, the other group of UEs is available for scheduling. FIG. 5shows an alternate configuration where the DMTC time window and the DRSoccasions have the same periodicity. However, each cell transmits DRSsin multiple instances of the DRS occasion and different groups of UEsare assigned different measurement gaps or DMTCs that align with one ofthe instances of the DRS occasion.

Beamforming

In order to enhance system capacity and to reduce interference, thenetwork node (e.g., base station or eNB) may use beamforming (i.e., UEsare served with transmit beams pointing in their direction). Thebeamforming is realized by virtue of a Multiple Input Multiple Output(MIMO) technique where a signal is transmitted in a beam by applying thesame signal to multiple co-located transmit antennas and applying aphase shift per transmit antenna. The phase shift determines thepointing direction of the transmit beam. MIMO implies that both thenetwork node and the UE employ multiple antennas, but it should be notedthat transmit beamforming from the network node can be used in case theUE has a single antenna as well.

The MIMO configuration is generally represented by a notation (M×N) interms number of transmit (M) and receive antennas (N). Common MIMOconfigurations used are: (2×1), (1×2), (2×2), (4×2), (8×2), and (8×4).The MIMO configurations represented by (2×1) and (1×2) are special casesof MIMO, and they correspond to transmit diversity and receiverdiversity respectively. In LTE Release 12 and Release 13, up to M=16 and32 is specified.

In order to create large number of sharp beams in vertical and azimuthdirections (aka three dimensional beams), the network node may employactive antennas (aka Active Antenna System (AAS)). The AAS systemcomprises an array of a large number of antenna elements with aparticular arrangement. For example, they can be arranged in the form ofuniform linear array, 2-dimensional matrix (columns and rows), circular,etc. The antenna elements are electronically controlled to enableelectronic amplification and/or other Radio Frequency (RF) processing.The electronic circuitry in a network node capable of the AAS systemallows substantial flexibility to dynamically control the beamcharacteristics such as direction, shape, and strength of the beams. Forexample, the beam's elevation and azimuth angles, beamwidth of theradiation pattern, etc. can be electronically controlled depending on,for example, the UE location.

SUMMARY

Systems and methods relating to transmission and use of DiscoveryReference Signal (DRS) signals are disclosed in herein. In someembodiments, a method of operation of a Transmission Point (TP) in acellular communications network comprises transmitting, from the TP, asame one or more DRS signals using at least two different transmit beamsin at least two different time resources. Each transmit beam ischaracterized by a direction in which it is transmitted. In this manner,the TP is enabled to reuse DRS resources, which in turn enablestransmission of DRS signals on a larger number of transmit beams and,correspondingly, adaptation of measurement procedures at wirelessdevices to obtain measurements on those transmit beams.

In some embodiments, transmitting the same one or more DRS signals usingthe at least two different transmit beams in the at least two differenttime resources comprises transmitting the one or more DRS signals usinga first transmit beam, but not a second transmit beam, in a first timeresource, and transmitting the one or more DRS signals using the secondtransmit beam, but not the first transmit beam, in a second timeresource. The second transmit beam is different than the first transmitbeam, and the second time resource is different than the first timeresource.

In some embodiments, the one or more DRS signals comprise a ChannelState Information Reference Signal (CSI-RS). In some embodiments, theone or more DRS signals comprise a Primary Synchronization Signal (PSS)for a Physical Cell Identity (PCI), a Secondary Synchronization Signal(SSS) for the same PCI, and a Common Reference Signal (CRS) for the samePCI. In some embodiments all DRS signals are beamformed. However in someembodiments only a subset of DRS signals are beamformed.

In some embodiments, each time resource of the at least two differenttime resources a time slot, a subframe, a symbol time, a frame, aTransmit Time Interval (TTI), or an interleaving time.

In some embodiments, the at least two different time resources are atleast two different DRS occasions, and transmitting the same one or moreDRS signals using the at least two different transmit beams in the atleast two different time resources comprises transmitting the same oneor more DRS signals using the at least two different transmit beams inthe at least two different DRS occasions.

In some embodiments, the at least two different time resources are atleast two time resources within a same DRS occasion, and transmittingthe same one or more DRS signals using the at least two differenttransmit beams in the at least two different time resources comprisestransmitting the same one or more DRS signals using the at least twodifferent transmit beams in the at least two different time resourceswithin the same DRS occasion.

In some embodiments, transmitting the same one or more DRS signals usingthe at least two different transmit beams in the at least two differenttime resources comprises transmitting the same one or more DRS signalsaccording to a DRS transmit beam pattern that defines the at least twodifferent transmit beams in the at least two different time resources inwhich the one or more DRS signals are to be transmitted. Further, insome embodiments, the DRS transmit beam pattern is a symmetric DRStransmit beam pattern. In other embodiments, the DRS transmit beampattern is an asymmetric DRS transmit beam pattern. In otherembodiments, the DRS transmit beam pattern is an aperiodic DRS transmitbeam pattern.

In some embodiments, transmitting the same one or more DRS signals usingthe at least two different transmit beams in the at least two differenttime resources comprises deciding that the one or more DRS signals areto be transmitted using a DRS transmit beam pattern, deciding which DRStransmit beam pattern is to be used for transmission of the one or moreDRS signals, and transmitting the same one or more DRS signals using theat least two different transmit beams in the at least two different timeresources in accordance with the DRS transmit beam pattern. Further, insome embodiments, deciding that the one or more DRS signals are to betransmitted using a DRS transmit beam pattern comprises deciding thatthe one or more DRS signals are to be transmitted using a DRS transmitbeam pattern based on one or more criteria selected from a groupconsisting of: a criterion that a request to use a DRS transmit beampattern is received from another network node; a criterion that a DRStransmit beam pattern is to be used when beamforming is used or isexpected to be used by the TP; a criterion that a DRS transmit beampattern is to be used when a number of transmit beams being used orexpected to be used by the TP is greater than a predefined threshold; acriterion that a DRS transmit beam pattern is to be used when there is alarge number of radio nodes in a coverage area of the TP; a criterionthat a DRS transmit beam pattern is to be used when there is a limitednumber of different DRS resources available; a criterion that a DRStransmit beam pattern is to be used for a particular deploymentscenario; a criterion that a DRS transmit beam pattern is to be usedwhen system load is greater than a predefined threshold; a criterionbased on measurement performance; and a criterion based on one or moreDRS transmission parameters.

In some embodiments, transmitting the same one or more DRS signals usingthe at least two different transmit beams in the at least two differenttime resources comprises transmitting the same one or more DRS signalsaccording to a DRS transmit beam pattern that defines the at least twodifferent transmit beams in the at least two different time resources inwhich the one or more DRS signals are to be transmitted. The methodfurther comprises providing information to a wireless device related totransmission of the one or more DRS signals in accordance with the DRStransmit beam pattern. In some embodiments, the information comprises anindication that the TP is or is expected to transmit DRS signalsaccording to a DRS transmit beam pattern. In some embodiments, theinformation comprises an indication that the TP is or is expected totransmit the one or more DRS signals according to the DRS transmit beampattern. In some embodiments, the information comprises informationrelated to transmission of DRS signals in accordance with DRS transmitbeam patterns in multiple cells.

In some embodiments, transmitting the same one or more DRS signals usingthe at least two different transmit beams in the at least two differenttime resources comprises transmitting the same one or more DRS signalsaccording to a DRS transmit beam pattern that defines the at least twodifferent transmit beams in the at least two different time resources inwhich the one or more DRS signals are to be transmitted. The methodfurther comprises providing information to another network node relatedto transmission of the one or more DRS signals, by the TP, in accordancewith the DRS transmit beam pattern.

In some embodiments, the method further comprises receiving one or moremeasurements from a wireless device based on the one or more DRS signalstransmitted using the at least two different transmit beams in the atleast two different time resources, and correlating each measurement ofthe one or more measurements to a respective one of the at least twodifferent transmit beams. Further, in some embodiments, transmitting thesame one or more DRS signals using the at least two different transmitbeams in the at least two different time resources comprisestransmitting the same one or more DRS signals according to a DRStransmit beam pattern that defines the at least two different transmitbeams in the at least two different time resources in which the one ormore DRS signals are to be transmitted. Correlating each measurement ofthe one or more measurements to the respective one of the at least twodifferent transmit beams comprises correlating each measurement of theone or more measurements to the respective one of the at least twodifferent transmit beams based on a known time resource in which themeasurement was obtained and the DRS transmit beam pattern.

Embodiments of a TP for a cellular communications network are alsodisclosed. In some embodiments, a TP includes a transceiver, aprocessor, and memory storing instructions executable by the processorwhereby the TP is operable to transmit, via the transceiver, a same oneor more DRS signals using at least two different transmit beams in atleast two different time resources. Each transmit beam is characterizedby a direction in which it is transmitted.

In some embodiments, a TP for a cellular communications network isadapted to transmit a same one or more DRS signals using at least twodifferent transmit beams in at least two different time resources. Eachtransmit beam is characterized by a direction in which it istransmitted. Further, in some embodiments, the TP is further adapted toperform the method of operation of a TP according to any of theembodiments described herein.

In some embodiments, a TP for a cellular communications networkcomprises a DRS transmission module operable to transmit a same one ormore DRS signals using at least two different transmit beams in at leasttwo different time resources. Each transmit beam being characterized bya direction in which it is transmitted.

Embodiments of a computer program are also disclosed. In someembodiments, a computer program comprises instructions which, whenexecuted on at least one processor, cause the at least one processor tocarry out the method of operation of a TP according to any of theembodiments described herein. Further, in some embodiments, a carriercontaining the aforementioned computer program is disclosed, wherein thecarrier is one of an electronic signal, an optical signal, a radiosignal, or a computer readable storage medium.

Embodiments of a non-transitory computer readable medium are alsodisclosed. In some embodiments, a non-transitory computer readablemedium stores software instructions that when executed by a processor ofa TP for a cellular communications network cause the TP to transmit asame one or more DRS signals using at least two different transmit beamsin at least two different time resources. Each transmit beam ischaracterized by a direction in which it is transmitted.

Embodiments of a method of operation of a wireless device in a cellularcommunications network are also disclosed. In some embodiments, a methodof operation of a wireless device comprises obtaining informationrelated to DRS transmission configuration. The information related toDRS transmission configuration comprising at least one of a groupconsisting of: DRS transmit beam pattern information that is related toa DRS transmit beam pattern used for one or more cells and measurementadaptation information used to adapt one or more measurement procedures.The method further comprises performing one or more measurements on oneor more DRS signals in accordance with the information related to DRStransmission configuration and using at least one of the one or moremeasurements for one or more radio operation tasks.

In some embodiments, the information related to DRS transmissionconfiguration comprises the DRS transmit beam pattern information, andthe DRS transmit beam pattern information comprises an indication ofwhether at least one TP for the one or more cells is or is expected totransmit DRS signals according to a DRS transmit beam pattern.

In some embodiments, the information related to DRS transmissionconfiguration comprises the DRS transmit beam pattern information, andthe DRS transmit beam pattern information comprises an indication of aDRS transmit beam pattern that is or is expected to be used fortransmission of a DRS resource for at least one of the one or morecells.

In some embodiments, the information related to DRS transmissionconfiguration further comprises at least one of a group consisting of:information related to physical resources in which a DRS signal istransmitted, a bandwidth of the DRS signal, a measurement bandwidth forthe DRS signal, and a periodicity of DRS occasions.

In some embodiments, obtaining the information related to DRStransmission configuration comprises obtaining the information relatedto DRS transmission configuration from a network node.

In some embodiments, obtaining the information related to DRStransmission configuration comprises obtaining the information relatedto DRS transmission configuration based on one or more predefined rules.

In some embodiments, obtaining the information related to DRStransmission configuration comprises obtaining the information relatedto DRS transmission configuration autonomously. In some embodiments,obtaining the information related to DRS transmission configurationautonomously comprises autonomously detecting whether different beamsare used for transmission in at least one of a group consisting of:different DRS occasions and different time resources within a DRSoccasion. In some embodiments, the method further comprises transmittingthe information related to DRS transmission configuration to at leastone of a group consisting of: a network node and another wirelessdevice.

In some embodiments, performing the one or more measurements comprisesadapting one or more measurement procedures based on the informationrelated to DRS transmission configuration in order to perform the one ormore measurements on the one or more DRS resources in accordance withthe DRS transmission configuration information. Further, in someembodiments, performing the one or more measurements comprises adaptingone or more measurement procedures based on the measurement adaptationinformation, and the measurement adaptation information comprises atleast one of a group consisting of: a layer 3 filtering coefficientwhose value is set such that DRS measurements made by the wirelessdevice are not averaged, and a time to trigger parameter whose value isset such that the time to trigger a DRS reporting event in the wirelessdevice is zero.

In some embodiments, adapting the one or more measurement procedurescomprises at least one of a group consisting of switching between afirst measurement mode for use when a DRS transmit beam pattern is notused for DRS transmission and a second measurement mode for use when aDRS transmit beam pattern is used for DRS transmission, reporting up toM measurements of different DRS resources but only M′<M measurementsobtained for a same time resource, and adapting at least one measurementprocedure to detect and differentiate between different beams that use asame DRS resource in different time resources.

In some embodiments, the one or more radio operation tasks comprise atleast one of a group consisting of: performing a cell change, reportingat least one of the one or more measurements to a network node,reporting at least one of the one or more measurements to anotherwireless device, and determining a position of the wireless device.

In some embodiments, the one or more radio operation tasks comprisereporting at least one of the one or more measurements to a network nodein association with an indication of a timing resource during which theat least one of the one or more measurements was obtained.

In some embodiments, the method further comprises signaling, to anetwork node, an indication of a capability of the wireless device tosupport transmission of DRS resources in accordance with a DRS transmitbeam pattern.

Embodiments of a wireless device for a cellular communications networkare also disclosed. In some embodiments, a wireless device comprises atransceiver, a processor, and memory storing instructions executable bythe processor whereby the wireless device is operable to obtaininformation related to DRS transmission configuration, the informationrelated to DRS transmission configuration comprising at least one of agroup consisting of: DRS transmit beam pattern information that isrelated to a DRS transmit beam pattern used for one or more cells, andmeasurement adaptation information used to adapt one or more measurementprocedures. The wireless device is further operable to perform one ormore measurements on one or more DRS signals in accordance with theinformation related to DRS transmission configuration, and use at leastone of the one or more measurements for one or more radio operationtasks.

In some embodiments, a wireless device for a cellular communicationsnetwork is adapted to obtain information related to DRS transmissionconfiguration, the information related to DRS transmission configurationcomprising at least one of a group consisting of: DRS transmit beampattern information that is related to a DRS transmit beam pattern usedfor one or more cells, and measurement adaptation information used toadapt one or more measurement procedures. The wireless device is furtheradapted to perform one or more measurements on one or more DRS signalsin accordance with the information related to DRS transmissionconfiguration, and use at least one of the one or more measurements forone or more radio operation tasks. In some embodiments, the wirelessdevice is further adapted to operate according to any of the embodimentsof the method of operation of a wireless device described herein.

In some embodiments, a wireless device for a cellular communicationsnetwork comprises an information obtaining module operable to obtaininformation related to DRS transmission configuration, the informationrelated to DRS transmission configuration comprising at least one of agroup consisting of: DRS transmit beam pattern information that isrelated to a DRS transmit beam pattern used for one or more cells, andmeasurement adaptation information used to adapt one or more measurementprocedures. The wireless device further comprises a measurement moduleoperable to perform one or more measurements on one or more DRSresources in accordance with the information related to DRS transmissionconfiguration, and a use module operable to use at least one of the oneor more measurements for one or more radio operation tasks.

Embodiments of a computer program are also disclosed. In someembodiments, a computer program comprises instructions which, whenexecuted on at least one processor, cause the at least one processor tocarry out the method of operation of a wireless device according to anyof the embodiments described herein. Further, in some embodiments, acarrier containing the aforementioned computer program is disclosed,wherein the carrier is one of an electronic signal, an optical signal, aradio signal, or a computer readable storage medium.

Embodiments of a non-transitory computer readable medium are alsodisclosed. In some embodiments, the non-transitory computer readablemedium stores software instructions that when executed by a processor ofa wireless device for a cellular communications network cause thewireless device to obtain information related to DRS transmissionconfiguration, perform one or more measurements on one or more DRSresources in accordance with the information related to DRS transmissionconfiguration, and use at least one of the one or more measurements forone or more radio operation tasks. The information related to DRStransmission configuration comprises at least one of a group consistingof: DRS transmit beam pattern information that is related to a DRStransmit beam pattern used for one or more cells, and measurementadaptation information used to adapt one or more measurement procedures.

Those skilled in the art will appreciate the scope of the presentdisclosure and realize additional aspects thereof after reading thefollowing detailed description of the embodiments in association withthe accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the disclosure, andtogether with the description serve to explain the principles of thedisclosure.

FIG. 1 illustrates a downlink physical resource in Third GenerationPartnership Project (3GPP) Long Term Evolution (LTE);

FIG. 2 illustrates a downlink subframe in 3GPP LTE;

FIG. 3 illustrates Resource Elements (REs) used by Discovery ReferenceSignal (DRS) signals in a Physical Resource Block (PRB) pair;

FIGS. 4 and 5 illustrate some possible configurations of DiscoveryMeasurement Timing Configurations (DMTCs) or measurement gaps thatsatisfy constraints related to DRS signals and DRS occasions;

FIG. 6 illustrates one example of a cellular communications network inwhich embodiments of the present disclosure may be implemented;

FIG. 7 is a flow chart that illustrates the operation of a TransmissionPoint (TP) according to some embodiments of the present disclosure;

FIG. 8 is a more detailed illustration of a process for transmitting thesame DRS signal(s) on different transmit beams in different timeresources according to some embodiments of the present disclosure;

FIG. 9 is a flow chart that illustrates the operation of a TP accordingto some other embodiments of the present disclosure;

FIG. 10 is a flow chart that illustrates the operation of a wirelessdevice according to some embodiments of the present disclosure;

FIG. 11 illustrates the operation of a TP and a wireless deviceaccording to some embodiments of the present disclosure;

FIG. 12 illustrates another example of a cellular communications networkin which embodiments of the present disclosure may be implemented;

FIGS. 13 and 14 are block diagrams of a wireless device according tosome embodiments of the present disclosure; and

FIGS. 15, 16, and 17 are block diagrams of a TP according to someembodiments of the present disclosure.

DETAILED DESCRIPTION

The embodiments set forth below represent information to enable thoseskilled in the art to practice the embodiments and illustrate the bestmode of practicing the embodiments. Upon reading the followingdescription in light of the accompanying drawing figures, those skilledin the art will understand the concepts of the disclosure and willrecognize applications of these concepts not particularly addressedherein. It should be understood that these concepts and applicationsfall within the scope of the disclosure and the accompanying claims.

Network Node: In some embodiments, the non-limiting term “network node”(also interchangeably referred to as node) is commonly used and refersto any type of network node which directly or indirectly communicateswith a wireless device (e.g., a User Equipment (UE)) in a wirelesscommunication network (e.g., a cellular communications network such as,e.g., a Third Generation Partnership Project (3GPP) Long Term Evolution(LTE) network). A network node can be a radio network node (alsoreferred to as a radio access node) in a radio access network, a corenetwork node in a core network, or a node in a fixed part of thenetwork. For example, a network node can be a network node serving awireless device (e.g., UE), a network node neighboring a serving networknode of a wireless device, or any network node in the radio accessnetwork or in the core network in a wireless communication system inwhich the wireless device operates. Examples of a network node are abase station, a Multi-Standard Radio (MSR) radio node such as a MSR basestation, an enhanced or evolved Node B (eNB), a network controller, aradio network controller, a base station controller, a relay, a donornode controlling relay, a Base Transceiver Station (BTS), an AccessPoint (AP), a core network node (e.g., a Mobile Switching Center (MSC),a Mobility Management Entity (MME), etc.), an Operations and Management(O&M) node, an Operations Support System (OSS) node, a Self-OrganizingNetwork (SON) node, a positioning node (e.g., an Evolved Serving MobileLocation Center (E-SMLC)), a Minimization of Drive Test (MDT) node, etc.

Wireless Device: In some embodiments, the non-limiting term “wirelessdevice” is used to refer to any type of wireless device communicatingwith a wireless communication system. One example of a wireless deviceis a UE. The term “UE” is a non-limiting term used herein to refer toany type of wireless device communicating with a network node in acellular or mobile communication system over radio interface. Examplesof UEs include a UE in a 3GPP LTE network, a target device, aDevice-to-Device (D2D) UE, a Machine Type Communication (MTC) UE, a UEcapable of Machine-to-Machine (M2M) communication, a Personal DigitalAssistant (PDA), an iPAD, a tablet, a mobile terminal, a smart phone,Laptop Embedded Equipment (LEE), Laptop Mounted Equipment (LME), aUniversal Serial Bus (USB) dongle, etc.

Discovery Reference Signal (DRS) or DRS Signal: As used herein, thenon-limiting term “DRS signal” is used interchangeably with the terms“DRS” and “discovery signal.” As used herein, the non-limiting term “DRSsignal” is any type of discovery signal transmitted in a wirelesscommunication network such as a cellular communications network. As anexample, in a 3GPP LTE network, a DRS signal is a DRS signal transmittedby a Transmission Point (TP) during a DRS occasion, and the DRS signalis a Primary Synchronization Signal (PSS), a Secondary SynchronizationSignal (SSS), a Common Reference Signal (CRS), a Channel StateInformation Reference Signal (CSI-RS), a Positioning Reference Signal(PRS), etc. transmitted by a TP in a DRS occasion. DRS signals can betransmitted in a cell in a DRS occasion (also referred to herein as a“discovery occasion”) with some periodicity (aka DRS occasionperiodicity or discovery occasion periodicity). A DRS occasion maycontain a certain number of time resources (e.g., subframes) with DRSsignals (e.g. between 1-6 subframes). Examples of a DRS occasionperiodicity include 40 milliseconds (ms), 80 ms, and 160 ms. A DRS maybe identified by a DRS index. A DRS index may be associated with aconfiguration of a DRS, such as one or more of its physical cell ID,scrambling identity, resource configuration (which OFDM symbols andsubcarriers in a subframe carry the DRS), and its subframe offset (whichsubframe of the subframes in a DRS occasion carry the DRS).

DRS Resource: As used herein, the term “DRS resource” (also referred toas a “discovery resource”) is a unique combination of DRS signal(s)(e.g., a unique combination of PSS, SSS, CRS, and CSI-RS). In otherwords, a DRS resource corresponds to one DRS configuration. Each DRSconfiguration configures one DRS resource including, for example, PSS,SSS, and potentially one CSI-RS.

DRS Occasion: As used herein, the term “DRS occasion” comprises one ormore time resources (e.g., subframes) during which a DRS signal(s) istransmitted. A DRS occasion is also referred to as a “discoveryoccasion,” “discovery signal occasion,” “discovery signal transmissionoccasion,” “discovery occasion reference signal occasion,” “positioningoccasion,” “PRS occasion,” etc.

Time Resource: In some embodiments, a non-limiting term “time resource”is used. As used herein, a “time resource” is any unit of time in awireless communication system (e.g., a cellular communications network).For example, a time resource can be a time slot, a subframe, a symbol, aframe, a Transmit Time Interval (TTI), an interleaving time, etc.

Measurement: In some embodiments, a non-limiting term “measurement” isused. The embodiments are applicable for any type of measurementperformed by a wireless device on any DRS signal. Examples ofmeasurements which can be performed by the wireless device on a DRSsignal(s) are cell search aka cell identification, Reference SignalReceived Power (RSRP), Reference Signal Received Quality (RSRQ), ChannelState Information RSRP (CSI-RSRP) (as defined in, e.g., 3GPP TS 36.214V12.2.0, Section 5.1.20), CSI-RSRQ, Channel Quality Indication (CQI),CSI, UE reception-transmission (Rx-Tx) time difference, Signal toInterference plus Noise Ratio (SINR), DRS-SINR, etc. CSI-RSRQ on linearscale is a ratio of CSI-RSRP to RSSI, where RSSI is the total receivedpower at the UE including all types of interference and noise. Ameasurement can be performed by the wireless device on one or moreserving cells and/or on one or more neighbor cells. A measurement canalso be performed on DRS signals transmitted by one or more TPs withinthe same cell, which can be a serving or neighbor cell. Therefore, oneor more measurements done on a cell or a network node may also beinterchangeably referred to as measurements done on the TP or signals ofthe TP.

Transmission or Transmit Point (TP): As used herein, the non-limitingterm “TP” refers to a network node with one or multiple co-locatedantennas associated with a cell identity (PCI). A network node (forexample an eNB or base station) may have a single TP or multiple,distributed TPs. A TP can be a serving or neighboring TP. A TP isinterchangeably referred to as a Remote Radio Head (RRH) and RemoteRadio Unit (RRU) or in the case of single TP as a base station or evenall network nodes in a shared cell can be termed as TPs.

While the systems and methods disclosed herein are applicable to anywireless communications technology, embodiments of the presentdisclosure are described in the context of 3GPP LTE technology. In otherwords, the embodiments described below focus on 3GPP LTE. As such, 3GPPLTE terminology is sometimes used. However, the embodiments areapplicable to any Radio Access Technology (RAT) or multi-RAT system,where the wireless device receives and/or transmits signals (e.g., data)e.g. LTE Frequency Division Duplexing (FDD)/Time Division Duplexing(TDD), Wideband Code Division Multiple Access (WCDMA)/High Speed PacketAccess (HSPA), Global System for Mobile Communications (GSM)/GSMEnhanced Data Rates for GSM Evolution (EDGE) Radio Access Network(GERAN), Wi-Fi, Wireless Local Area Network (WLAN), Code DivisionMultiple Access 2000 (CDMA2000), etc.

A problem with using DRS features in a beamformed system is that thenumber of available DRS resources is insufficient since each node mayhave a large number of possible transmit beams and each transmit beam isassociated with a unique DRS resource. In the beamformed system, thenetwork node may have a large number of antennas, which can be used togenerate several transmit beams in the same cell. One solution toproviding a unique DRS resource for each transmit beam is to increasethe number of DRS resources. However, increasing the number of DRSresources in the beamformed system will significantly increase signalingoverhead due to a potentially large number of transmit beams.

Embodiments of the present disclosure address the aforementionedproblems in a beamformed system. Embodiments of the present disclosureare directed to signaling, from a network node to a UE, informationabout transmit beams (aka transmission beams) used for transmitting thesame DRS signal(s) (i.e., transmit beams using the same DRS resource)using two or more transmit beams in different time resources. Thissignaling allows the UE to adapt its measurement procedure when doingmeasurements on DRS signal(s), e.g. averaging of samples used forobtaining the results. The UE may also signal the time instant when theDRS measurement was made to accompany the DRS based (CSI-RSRP)measurements and an identifier of the DRS configuration associated withthe DRS measurement, such as a DRS index (which may, in someembodiments, be a CSI-RS ID that identifies a CSI-RS configuration).

The measurement performance is enhanced as a result of beam specificmeasurements even when a large number of beams are used by the networknode. This in turns enhances the UE mobility performance.

The density of reference signal structures that are developed forregular deployments with existing systems such as 3GPP LTE may be highsuch that there is a lot of unnecessary interference created whendeployments become dense. Reference signals may be transmitted even whenthere is no data being sent to UEs.

A set of reference signals that are sent with much lower density in timehave been introduced in 3GPP with the intention being for this set ofreference signals to be used for small cells. Such signals are referredto as DRS signals (aka discovery signals or DRSs) and proceduresassociated with them are referred to as DRS procedures or discoveryprocedures.

Another motivation for the DRS signals/procedures is to facilitate theefficient measurement of received signal strength and quality (referredto in 3GPP as RSRP and RSRQ) for different TPs within a cell. These TPsmay be geographically separated (i.e., in separate geographic locations)but perform coordinated transmissions as a logical single cell entity.

In the present disclosure, a new application of DRS signals is used,where different DRS signals are used for different transmit beamstransmitted from the same TP. A transmit beam is generated by an arrayof antenna elements, where the same signal is transmitted from theantenna elements but with different adaptive phase shifts in order tosteer the transmit beam in the desired direction while reducinginterference towards other directions.

A TP can in principle generate an arbitrarily large set of beams, or afinite set of beams can also be used. In general, the array of antennaelements may be two or three dimensional and the set of transmit beamsmay have pointing directions in azimuth and elevation, so calledtwo-dimensional (2D)-beamforming.

Advantages of embodiments of the present disclosure are readilyidentifiable to those of ordinary skill in the art. These advantagesinclude, but are not limited to:

Allowing for a much larger set of transmit beams (DRSs) to be used inthe system, which is useful when a dense set of nodes, each employingbeamforming, is used.

The solution enables the UE to know whether the transmit beams are thesame or different in different time resources, e.g. in different DRSoccasions. This enables the UE to adapt one or more measurementprocedures.

Systems and methods relating to transmission of DRSs by a TP on multipletransmit beams are disclosed. In addition, systems and methods relatingto performing measurements on DRS signals and adapting measurementprocedures based on information relating to DRS transmissionconfiguration are also disclosed. In this regard, FIG. 6 illustrates oneexample of a cellular communications network 10 in which embodiments ofthe present disclosure may be implemented. Note that the cellularcommunications network 10 is only one example and is to be understood asbeing non-limiting. As illustrated, the cellular communications network10 includes a macro node 12 (e.g., a base station such as, e.g., an eNB)serving a macro cell 14 and a number of RRHs 16-1 through 16-3(generally referred to herein collectively as RRHs 16 and individuallyas RRH 16) serving respective small cells 18-1 through 18-3 (generallyreferred to herein collectively as small cells 18 and individually assmall cell 18). The cellular communications network 10 is a shared celldeployment in which the macro cell 14 and the small cells 18 share thesame cell Identity (ID) (e.g., the same Physical Cell ID (PCI)). Themacro node 12 and the RRHs 16 provide radio access to a number ofwireless devices 20-1 through 20-4 (generally referred to hereincollectively as wireless devices 20 and individually as wireless device20).

With respect to a wireless device 20, the cells 14 and 18 may be on aserving carrier (i.e., be serving cells of the wireless device 20) or anon-serving carrier (i.e., be non-serving cells of the wireless device20). Examples of serving carriers are a Primary Component Carrier (PCC),also known as a Primary Cell (PCell), and a Secondary Component Carrier(SCC), also known as a Secondary Cell (SCell), in Carrier Aggregation(CA) (aka multi-carrier), a Primary Secondary Component Carrier (PSCC),and a SCC in Dual Connectivity (DC). Examples of non-serving carriersare inter-frequency carriers, inter-RAT carriers, etc. Note thatmeasurements on non-serving carriers can be performed using measurementgaps or without measurement gaps.

According to some embodiments of the present disclosure, one or multipleTPs (e.g., one or more macro nodes 12 and/or one or more RRHs 16) eachtransmit multiple beams (transmit beams) and each transmit beam isassociated with a DRS resource. Currently, in 3GPP LTE, only 96 uniqueDRS resources are supported in Release 12 (Rel-12), and Rel-12 has beendesigned for a network with a rather small number of TPs in a given areawith one DRS resource per TP. An example of a smaller set of TPs is 2 or3. In particular, as discussed above, considering that a DRS occasionmay be up to 5 subframes long in an FDD frame structure, the largestpossible number of CSI-RS RE configurations is 96. This means that thelargest possible number of unique DRS resources is 96. Further, itshould be noted that, at least in some embodiments, only CSI-RS isbeamformed (i.e., PSS, SSS, and CRS may not be beamformed) while, inother embodiments, both CSI-RS (if configured) and one or more other DRSsignals (e.g., PSS, SSS, and/or CRS) are beamformed.

If each TP has multiple transmit beams, there is a need for even morethan 96 DRS resources. Embodiments of the present disclosure relate toreusing DRS resources in time such that the DRS signals for a particularDRS resource with index Q are transmitted in a transmit beam A at timeinstant A and the same DRS signals (for the same DRS resource with indexQ) are transmitted in another transmit beam B, different from transmitbeam A, at another time instant B. The same DRS signals (i.e., the DRSsignals corresponding to the same DRS resource) may comprise DRS signalsfor the same identifier, e.g. a PSS, SSS or CRS for the same PCI (wherea particular PCI is mapped to a particular PSS, SSS, or CRS as will beappreciated by one of ordinary skill in the art), a CSI-RS for the sameidentifier of the TP transmitting the CSI-RS, etc.

This transmission of the same DRS signals on at least two differenttransmit beams at two different times (i.e., in two different timeresources) is termed herein as a pattern. The pattern is morespecifically referred to herein as a DRS transmit beam pattern. Withinthe DRS transmit beam pattern, the same DRS resource is used (i.e., thesame DRS signals are transmitted so that the PSS, SSS, and CSI-RS (ifconfigured) occupy the same resource elements in the subframe containingDRS, but in the two different subframes e.g. with same cell ID, TP ID,etc.). The embodiments are applicable for the DRS transmission patterncomprising of any number of transmit beams, e.g. transmit beams A, B, C,D, E, and so on.

A DRS transmit beam pattern comprises the transmission of the same oneor more DRS signals in at least two different transmit beams (e.g., Aand B) in at least two different time resources (e.g., two different DRSoccasions). The DRS transmit beam pattern is also characterized by areference time parameter. Examples of the reference time parameter forthe DRS transmit beam pattern are a starting time of the pattern, alength of the pattern in time, an ending time of the pattern, etc. Thestarting time of the pattern can be expressed in terms of a frame numberor an absolute or global reference time such as Global NavigationSatellite System (GNSS) reference time (e.g., Global Positioning System(GPS) reference time). An example of a frame number as the referencetime is a System Frame Number (SFN), which is repeated with a cycle(e.g., after every 1024 radio frames). Therefore, the SFN may vary from0 to 1023. For example, a starting reference time of a pattern can beconfigured by a network node or can be predefined. Examples ofpredefined SFNs are SFN=0, SFN=512, etc.

-   As an example, the pattern of beams A and B using the same DRS    signals are transmitted in two successive time resources and are    repeated in subsequent time resources, i.e. in subsequent DRS    occasions. Typically, the beams with the same characteristics (e.g.,    direction, beam width, etc.) are repeated periodically. For example,    assume that the same DRS signals can be transmitted in four    different beams (namely A, B, C, and D) in four consecutive DRS    occasions (namely T0, T1, T2, and T3, respectively). As an example,    each DRS occasion contains 1 subframe and each DRS occasion occurs    periodically once every 40 ms. The same DRS signals (e.g.,    PSS/SSS/CRS, CSI-RS, etc.) are transmitted in the same direction as    transmit beams A, B, C, and D in the subsequent DRS occasions,    namely T4, T5, T6, and T7, respectively. This is an example of a    symmetric periodic pattern with a period of 4 DRS occasions and    where within each pattern period all possible beams are transmitted    with equal probability and the contents of the pattern is the same    in all pattern periods.

An example of a symmetric periodic DRS transmit beam pattern isexpressed below by (1) and (2):DRS occasions: [{T0,T1,T2,T3},{T4,T5,T6,T7}, . . . ]  (1)Beams/occasion: [{A,B,C,D},{A,B,C,D} . . . ]  (2)Another example of a symmetric periodic DRS transmit beam pattern isexpressed below by (3) and (4). In this case, each beam is repeated overtwo consecutive DRS occasions within a period of the pattern equal to 8.DRS occasions:[{T0,T1,T2,T3,T4,T5,T6,T7},{T8,T9,T10,T11,T12,T13,T14,T15}, . . . ]  (3)Beams/occasion: [{A,A,B,B,C,C,D,D},{A,A,B,B,C,C,D,D}, . . . ]  (4)

The periodic pattern can also be asymmetric (asymmetric periodic DRStransmit beam pattern) where the pattern period is the same but contentsof patterns in different periods can be different. An example of such apattern with a period of 6 DRS occasion is expressed below by (5) and(6):DRS occasions: [{T0,T1,T2,T3,T4,T5},{T6,T7,T8,T9,T10,T11} . . . ]  (5)Beams/occasion: [{A,A,B,B,C,D},{C,D,D,D,A,B} . . . ]  (6)

In some embodiments the DRS transmit beam pattern can also be aperiodicwhere the period can change after every pattern. An example of such apattern is expressed below by (7) and (8):DRS occasions: [{T0,T1,T2},{T3,T4,T5,T6,T7},{T8,T9,T10,T11} . . . ]  (7)Beams/occasion: [{A,B,C},{B,C,D,D,A},{C,D,D,D,A} . . . ]  (8)

In yet another example of a DRS transmit beam pattern, different beamsusing the same DRS resource (i.e., transmitting the same DRS signal(s))are used in different time resources (e.g., different subframes) withinthe same DRS occasion. In one implementation, the same DRS transmit beampattern can be used in different DRS occasions. However, in someimplementations, a different DRS transmit beam pattern can also be usedin different DRS occasions. An example of such a DRS transmit beampattern (i.e., different beams within the same DRS occasion) isexpressed below by (9) and (10). In this example, it is assumed that oneDRS occasion contains 4 time resources (e.g., 4 subframes) containing 4different beams: A, B, C, and D:Time resources within one DRS occasion: {t0,t1,t2,t3}  (9)Beam/time resource: {A,B,C,D}  (10)

In yet another example of a DRS transmit beam pattern within a DRSoccasion, different beams on the same DRS resource are used in differenttime resources (e.g., different subframes) within the same DRS occasionbut some of them are repeated. An example of such a DRS transmit beampattern is expressed below by (11) and (12). In this example, it isassumed that one DRS occasion contains 6 time resources (e.g., 6subframes) containing 4 different types of beams: A, B, C, and D.However, two of the 4 beams are transmitted twice:Time resources within one DRS occasion: {t0,t1,t2,t3,t4,t5}  (11)Beam/time resource: {A,B,B,C,D,D}  (12)

In some embodiments, it is up to a network node (e.g., the macro node12) to decide whether or not the DRS signals should be transmitted usinga DRS transmit beam pattern or without a DRS transmit beam pattern(i.e., like in conventional or existing systems). When using a DRStransmit beam pattern for DRS transmission, it is also up to the networknode to decide which type of DRS transmit beam pattern is to be used fortransmitting the DRS signals. The DRS signals are eventually used by thewireless device 20 for performing measurements on the DRS signals.

According to some embodiments, a network node may decide to generate aDRS transmission pattern (i.e., to transmit DRS signals according to aDRS pattern) and also decide the type of DRS transmission pattern basedon one or more of the following criteria:

A criterion related to reception of a request from another network node,e.g. a TP is requested to use a DRS transmission pattern and/or a typeof DRS transmission pattern by a serving eNB;

A criterion related to when beam forming is being used or expected to beused by the network node (e.g., use a DRS transmission pattern when beamforming is being used or expected to be used);

A criterion related to the number of transmit beams being used orexpected to be used by the network node (e.g., use a DRS pattern whenthe number of beams being used or expected to be used by the networknode is larger than a threshold);

A criterion related to the number of radio nodes in the coverage area(e.g., use a DRS pattern when there is large number (e.g., more than athreshold number) of radio nodes in the coverage area, e.g. a largenumber of TPs per shared cell, i.e. with the same PCI);

A criterion related to the number of available DRS resources and/or thenumber of unavailable DRS resources (e.g., use a DRS transmissionpattern when there is a limited number (e.g., less than a thresholdnumber) of different DRS resources that are available or when there issome threshold number of DRS resources that cannot be used);

A criterion related to the deployment scenario (e.g., use a DRStransmission pattern in a certain deployment scenario(s), e.g. a cellserving a high rise building where the wireless devices 20 aredistributed in both azimuth and vertical directions);

A criterion related to system load (e.g., use a DRS transmission patternwhen system load is high, e.g. a large number of wireless devices 20 inthe cell);

A criterion related to measurement performance: To enable the wirelessdevice 20 to achieve better measurement accuracy, the network node mayuse a symmetric periodic pattern with more than one repetition of thesame beam in the same pattern period; and/or

A criterion related to DRS transmission parameters. For example, if DRSbandwidth is larger than a threshold (e.g., 50 Resource Blocks (RBs) ormore) the network node may use a symmetric periodic pattern with norepetition of the same beam in the same pattern period.

In some embodiments, a network node (e.g., the macro node 12), wheninitiating DRS transmission according to a DRS transmission pattern, mayalso transmit information to one or more wireless devices 20. Theinformation is used to inform the wireless device(s) 20 that the networknode is transmitting or expected to transmit DRS according to a DRStransmission pattern (generally) or according to a specific transmissionpattern. The network node, when stopping DRS transmission according tothe DRS transmission pattern, may also send corresponding information(i.e., about ceasing transmission of DRS signals according to the DRStransmission pattern) to the wireless device(s) 20.

In one example, the information may comprise an indicator that indicateswhether the network node is:

transmitting (or expected to transmit) DRS signals with (according to) aDRS transmit beam pattern, or

stopping (or expected to stop) an ongoing DRS transmission with(according to) a DRS transmit beam pattern.

In another example, the information may provide at least some indicationabout the DRS transmit beam pattern being used or expected to be used orbeing stopped for transmitting DRS signals. Examples of such informationabout the pattern are:

A predefined identifier of one of multiple predefined DRS transmit beampatterns and a pattern reference time such as a starting time of thepattern, e.g. SFN=4;

Partial or complete information about the pattern itself. This maycomprise one or more of: a pattern reference time such as a startingtime of the pattern, a pattern periodicity, a type of pattern (e.g.,periodic or aperiodic, etc.), a number of distinct or different beamsused in the same pattern for the same DRS resource, etc.

Any of the above mentioned information may be associated with one ormultiple cells, e.g. for one or more serving cells and/or for one ormore neighbor cells of a wireless device 20. For example, the networknode may signal information for multiple cells to the wireless device20, thereby enabling the wireless device 20 to measure on multiplecells. In some embodiments, the signaled information for each cell mayalso include a cell ID and/or cell related information, e.g. PCI, TP ID,etc. In some embodiments, the signaled information may be common formultiple cells, e.g. the same information is applicable for all cells onthe same carrier frequency. In some embodiments, the signaledinformation may be common for two or more carrier frequencies, e.g. thesame information is applicable for all cells on the serving carrierfrequency and for all cells on one or more non-serving carrierfrequencies such as inter-frequency carriers.

The network node may transmit the aforementioned information to thewireless device(s) 20 using higher layer signaling such as RadioResource Control (RRC) or Media Access Control (MAC) signaling. Thenetwork node may transmit this information in a broadcast message forall or a group of wireless devices 20 in the respective cell or tospecific wireless devices 20 in wireless device specific (aka dedicated)messages. The wireless devices 20 may use this information to adapttheir measurement procedure(s), as described below.

According to some embodiments of the present disclosure, the networknode, when initiating a DRS transmission according to a DRS transmissionpattern or when ceasing an ongoing DRS transmission according to a DRStransmission pattern, may also transmit corresponding information to oneor more other network nodes, e.g. neighboring network nodes. Thecontents of the information about staring or stopping the DRS transmitbeam pattern can be the same as transmitted to the wireless device(s)20, which is described above. The network node receiving thisinformation may use this information for one or more tasks. Examples ofsuch tasks are: to create its own DRS transmission pattern; to decidewhether or not to transmit DRS signals according to the DRS transmissionpattern; and to inform the wireless devices 20 in the cell about the DRStransmission pattern used in neighboring network nodes, etc.

FIG. 7 is a flow chart that illustrates the operation of a TP (e.g., themacro node 12 or one of the RRHs 16 of FIG. 6 ) according to someembodiments of the present disclosure. The process of FIG. 7 illustratesat least some of the embodiments described herein. Note that dashedboxes represent optional steps that may or may not be included in theprocess, depending on the embodiment. As illustrated, in someembodiments, the TP receives capability information from one or morewireless devices 20 that indicates whether the wireless devices 20 havethe capability to, e.g., perform measurements on DRS signals transmittedaccording to a DRS pattern (step 100).

The TP transmits the same DRS signal(s) using at least two differenttransmit beams in at least two different time resources (e.g., accordingto a DRS transmit beam pattern), as described above (step 102). In someembodiments, the transmission in step 102 includes deciding whether aDRS transmit beam pattern is to be used (step 102A), deciding on a DRStransmit beam pattern to use (e.g., the type of DRS transmit beampattern) (step 102B), and transmitting the same DRS signal(s) on atleast two different beams in at least two different time resources inaccordance with the DRS transmit beam pattern (step 102C), as describedabove.

As illustrated in FIG. 8 , step 102 or step 102C includes, at least insome embodiments, transmitting the DRS signal(s) on a first transmitbeam, but not on (at least) a second transmit beam, in a first timeresource (e.g., in a first DRS occasion) (step 200). The TP transmitsthe same DRS signal(s) on the second transmit beam, but not (at least)the first transmit beam, in a second time resource (e.g., a second DRSoccasion (step 202). The first and second transmit beams are differenttransmit beams (i.e., have different beam directions), and the first andsecond time resources are different time resources (e.g., different DRSoccasions). Additional similar steps may be performed if more than twotransmit beams and/or more than two time resources are included in theDRS transmit beam pattern. Using this process, when, for example,transmitting the DRS signal(s) on the first transmit beam in the firsttime resource, the TP does not transmit the same DRS signal(s) on thesecond transmit beam and potentially not on any other transmit beam. Inparticular, when transmitting the DRS signal(s) on the first transmitbeam in the first time resource, the TP does not transmit the same DRSsignal(s) on any other transmit beam that would negatively impact theability of the wireless device(s) to perform measurements on the DRSsignal(s) transmitted on the first transmit beam. In the same manner,when transmitting the same DRS signal(s) on the second transmit beam inthe second time resource, the TP does not transmit the same DRSsignal(s) on the second transmit beam and potentially not on any othertransmit beam.

Returning to FIG. 7 , in some embodiments, the TP signals or otherwiseprovides information related to DRS transmission configuration to thewireless device(s) 20 and/or another network node (step 104), asdescribed above. In some embodiments, the TP receives one or moremeasurements from the wireless device 20 based on the transmitted DRSsignal(s) and correlates the measurement(s) to the respective transmitbeam(s) (step 106). As discussed below in detail, in some embodiments,an indication of a time resource for which the measurement(s) wereobtained is provided with or in association with the measurement(s).This timing information can then be used together with the DRS transmitbeam pattern to determine the transmit beam(s) to which themeasurement(s) apply. Examples of measurements which can be receivedfrom the wireless device 20 are cell search, a.k.a. cell identification,measurements such as RSRP, RSRQ, CSI-RSRP, CSI-RSRQ, CQI, CSI, UEreception-transmission time difference, SINR, DRS-SINR, etc.

In some embodiments, the TP uses the measurement(s) (step 108). Forexample, the TP may use the measurement(s) received from the wirelessdevice 20 by selecting one of the reported beams from the wirelessdevice 20 (identified by the DRS identity) and transmitting the downlinkshared data channel to the wireless device 20 using the same beam as thebeam used for the DRS beam for which the wireless device 20 has provideda measurement report.

FIG. 9 is a flow chart that illustrates the operation of a TP accordingto some embodiments of the present disclosure. As illustrated, the TPdecides that a DRS transmit beam pattern is not to be used fortransmission of DRS signals (step 300). Upon making this decision, theTP stops transmission of the DRS signals in accordance with the DRStransmit beam pattern (step 302) and signals an indicator to thewireless device(s) 20 that indicates the stoppage (step 304), asdescribed above.

Embodiments related to the operation of a wireless device 20 are alsodisclosed. In particular, systems and methods are disclosed that relateto performing measurements, at the wireless device 20, using DRSsignal(s) transmitted by a TP according to the embodiments describedabove (e.g., according to a DRS transmit beam pattern). In someembodiments, a method of operation of the wireless device 20 comprisesthe following two steps:

The wireless device 20 obtains at least information about (i.e., relatedto) the DRS transmission configuration, which comprises at leastinformation about one or more DRS transmit beam patterns used in one ormore cells (i.e., information about the pattern as described above); and

The wireless device 20 uses the obtained information for performing oneor more measurements on one or more DRS signals.

After performing one or more measurements, the wireless device 20 mayuse the one or more measurements for one or more radio operation tasks.Examples of such radio operation tasks are:

Performing cell change. Examples of cell change are handover, cellselection, cell reselection, RRC connection release with redirection,etc.;

Transmitting the measurement results to a network node (e.g., the TP).The wireless device 20 may send the measurement results using one ormore of the following mechanisms: periodically, event triggered basis,and event triggered periodic basis;

Transmitting the measurement results to another wireless device 20 ifthe wireless devices 20 are D2D capable (aka wireless devices 20 capableof Proximity Services (ProSes)). The wireless device 20 may send themeasurement results using one or more of the following mechanisms:periodically, event triggered basis, and event triggered periodic basis;

Using the measurement results for determining the position of thewireless device 20 (i.e., determining wireless device position).

The obtained information about the DRS transmission configuration mayalso contain additional data or contents related to DRS. For example,the additional information may be related to physical resources in whichDRS signals are transmitted. Examples of physical resources are timeresources containing DRS signals (e.g., the number of subframes per DRSoccasion), bandwidth of the DRS signals, measurement bandwidth of DRSsignals, periodicity of DRS occasions, etc. The wireless device 20 mayobtain any information about the DRS transmission configuration by oneor more of the following means:

In one exemplary implementation, the wireless device 20 may obtain theinformation by receiving the information from a network node (e.g., theTP) as described above;

In another exemplary implementation, the wireless device 20 may obtainthe information based on one or more predefined rules and/orinformation;

In yet another exemplary implementation, the wireless device 20 mayobtain the information autonomously. For example, the wireless device 20may autonomously detect whether or not beams are the same or aredifferent in different DRS occasions and/or in different time resourceswithin the same DRS occasion. The wireless device 20 may detect this by,for example, detecting the Angle of Arrival (AoA) of signals. In case ofdifferent beams, the wireless device 20 may detect a change in the AoAof signals and/or the signal strengths in different DRS occasions and/ortime resources per DRS occasion.

If the wireless device 20 autonomously detects one or more parametersrelated to the DRS transmission configuration (e.g., the number of beamsper DRS occasion, etc.), then the wireless device 20 may also transmitsuch autonomously obtained information to the network node and/or toanother wireless device 20.

In order to perform one or more measurements on DRS signals, thewireless device 20 may adapt one or more measurement procedures based onthe obtained information related to the DRS transmission configuration.For example, the adaptation of one or more measurement procedures willallow the wireless device 20 to perform measurements when the same DRSsignal(s) is used in different beams in different time resources, e.g.different DRS occasions and/or in different time resources in the sameDRS occasion. The adaptation may also depend on the type of informationrelated to DRS transmission configuration obtained by the wirelessdevice 20. The adaptation may also depend on the type of DRS transmitbeam pattern used by one or more cells on which the wireless device 20performs one or more measurements.

Some examples of such adaptations of measurement procedures in thewireless device 20 are now described. One example of such as adaptationis switching between a first measurement mode and a second measurementmode based on the obtained information related to the DRS transmissionconfiguration. In one example, in the first measurement mode, thewireless device 20 uses a first number of measurement samples to beaveraged over a Layer 1 (L1) measurement period to obtain measurementresults, whereas, in the second measurement mode, the wireless device 20uses a second number of measurement samples to be averaged over the L1measurement period to obtain measurement results. For example, if a DRStransmit beam pattern is used, then the wireless device 20 uses thefirst measurement mode where only one sample is used for obtaining themeasurement result. But if a DRS transmit beam pattern is not used, thenthe wireless device 20 uses the second measurement mode where two ormore samples in different DRS occasions are used for obtaining themeasurement result. In another example of the first measurement mode,the wireless device 20 may use two or more measurement samples but onlyon DRS signals transmitted using the same beam in different timeresource and/or DRS occasions. In yet another example, when using thefirst measurement mode, the wireless device 20 performs measurement overthe L1 measurement period, which is shorter than the L1 measurementperiod used for doing measurements with the second measurement mode.

In some embodiments, the wireless device 20 associates the results ofmeasurements with at least the timing related to the DRS transmission.For example, after the measurement when the wireless device 20 sends themeasurement report to a network node (e.g., the TP such as the macronode 12 (e.g., eNB)), the wireless device 20 reports the measured value,the DRS index Q, plus the time instant of the measurement (A or B). Insome embodiments, the DRS index comprises an identifier for a CSI-RSsuch as a MeasCSI-RS-Id-r12 information element 3GPP TechnicalSpecification (TS) 36.331 Section 6.3.5 (version 12.5.0). In oneembodiment, the time instant is given by the SFN or by any other framenumbering or group of multiple frame numbering. In one aspect of thisembodiment, the reported time instant is the start time instant (or endtime instant), in case the same DRS is transmitted in the same beam atmultiple time instants. For example, if DRS signal(s) on whichmeasurement is done and the SFN of that DRS occasion is 4, then thewireless device 20 signals the measurement results as well as at leastSFN=4. In another example of this embodiment, the timing instant iscomplemented by a disabling of the cross-frame or subframe averaging ofDRS measurements at the physical layer. This disabling may be signaledto the wireless device 20 by higher layers, such as RRC signaling. Thisdisabling may further set Layer 3 (L3) filtering of the DRS measurementsto zero, i.e. setting the variable a in 3GPP Technical Specification(TS) 36.331 (version 12.5.0) Section 5.5.3.2 to a=1. Furthermore, ifevent triggered DRS reporting is configured, the disabling may also setthe time to trigger the event to zero, i.e., set the information elementTimeToTrigger from 3GPP TS 36.331 (version 12.5.0) Section 6.3.5 toTimeToTrigger=ms0. In this manner, physical or higher layer filtering ofDRS measurements or triggering delays will not increase the timeambiguity of when the measurement occurred, and the network will bebetter able to identify which beam was transmitted.

As another example of the adaptation that may be performed by thewireless device 20, in some embodiments, the wireless device 20 isallowed to report M measurements of different DRS signals but only M′<Mmeasurements obtained at the same time index. With this solution, thenetwork node (e.g., eNB) may transmit beams from different TPs atdifferent time instants and thus get DRS measurements from multiple TPs.If this constraint would not be applied, the wireless device 20 may onlyreport measurements for beams at the TP closest to the wireless device20 (i.e., strongest received signal). Alternatively, the network node(e.g., eNB) may transmit DRS beams in different sectors of the cell atdifferent time instants, for the same reasons as for different TPs.

As another example, in some embodiments, the wireless device 20 mayadapt its procedure in order to be able to detect and differentiatebetween different beams using the same DRS resources (i.e., transmittingthe same DRS signal(s)) in different time resources, i.e. in differentDRS occasions and/or DRS time resources. For example, based on thisdetection, the wireless device 20 may use the performed measurements toidentify a number N of measurements with N most distinct beams, e.g.which have the most distinct direction in vertical and/or azimuthangles. The wireless device 20 may use N such measurements for one ormore radio operation tasks, e.g. for cell change, report N number ofmeasurements with N most distinct beams to the network node and/or toanother wireless device 20, for positioning, etc.

The wireless device 20 may adapt one or more of the above measurementprocedures based one or more of the following:

Request or indication received from the network node;

Autonomous decision by the wireless device 20. The wireless device 20may also perform the adaptation to comply to one or more predefinedrequirements;

One or more predefined rules specified in a standard. The predefinedrule may also be expressed in terms of one or more predefinedrequirements. For example, the wireless device 20 may have to adapt oneor more measurement procedures in order to meet one or more predefinedwireless device requirements related to wireless device measurements(aka measurement requirements), Radio Resource Management (RRM)requirements, mobility requirements, positioning measurementrequirements, etc. Examples of wireless device requirements related towireless device measurements are measurement time, measurement reportingtime or delay, measurement accuracy (e.g., RSRP/RSRQ accuracy), numberof cells to be measured over the measurement time, etc. Examples ofmeasurement time are L1 measurement period, cell identification time orcell search delay, Cell Global Identity (CGI) acquisition delay, etc.

According to another aspect, the procedure in the wireless device 20 maycomprise signaling, to the network node, one or more sets of informationrelated to a capability associated with obtaining a DRS transmit beampattern and using the DRS transmit beam pattern for one or moremeasurements. This is due to the fact that all wireless devices 20 mayor may not be capable of obtaining and using a DRS transmit beam patternfor measurements or may be capable of obtaining and using only aspecific type(s) of DRS transmit beam patterns. Based on such receivedwireless device capabilities, the network node may decide whether or notto configure the wireless device 20 with a DRS transmit beam pattern.The network node may also use additional information in the wirelessdevice capability to decide the actual DRS transmit beam pattern to beconfigured in the cell. The network node may also signal the receivedwireless device capability information to another network node. Thenetwork node may acquire the wireless device capability from thewireless device 20 and/or from another network node that contains suchinformation.

FIG. 10 is a flow chart that illustrates the operation of a wirelessdevice 20 according to some embodiments of the present disclosure. Theprocess of FIG. 10 illustrates at least some of the embodimentsdescribed herein. Note that dashed boxes represent optional steps thatmay or may not be included in the process, depending on the embodiment.As illustrated, in some embodiments, the wireless device 20 sendscapability information to a network node that indicates whether thewireless device 20 has the capability to obtain and use a DRS transmitbeam pattern (step 400), as described above.

The wireless device 20 obtains information related to a DRS transmissionconfiguration for one or more cells (step 402). As described above, thisinformation includes DRS transmit beam pattern information and/ormeasurement adaptation information for one or more cells. Themeasurement adaptation information may include, for example, an L3filtering coefficient whose value is set such that DRS measurements madeby the wireless device 20 are not averaged and/or a time to triggerparameter whose value is set such that the time to trigger a DRSreporting event in the wireless device 20 is zero. The information maybe obtained by the wireless device 20 in any suitable manner such as,for example, from a network node, from a predefined rule(s) and/orpredefined information, and/or autonomously. In some embodiments, thewireless device 20 transmits the obtained information or some subsetthereof to a network node or another wireless device 20 (step 404).

Based on the obtained information, the wireless device 20 performs oneor more measurements on a DRS signal(s) transmitted by one or more TPs,as described above (step 406). Performing the measurement(s) may includeadapting one or more measurement procedures. For example, as describedabove, this adaptation may be switching between two or more measurementmodes, reporting only M′<M measurements obtained at the same timeinstant, and/or detecting and differentiating between different beamsusing the same DRS resource in different time resources.

The wireless device 20 uses the measurement(s) for one or more radiooperation tasks (step 408). As described above, the one or more radiooperation tasks may include, for example, performing a cell change,reporting (i.e., transmitting) the measurement(s) to a network node,reporting (i.e., transmitting) the measurement(s) to another wirelessdevice 20, and/or determining the position of the wireless device 20.

FIG. 11 illustrates the operation of a TP 22 and a wireless device 20according to some embodiments of the present disclosure. As illustrated,the TP 22 transmits the same DRS signal(s) using at least two differenttransmit beams in at least two different time resources, e.g., inaccordance with a DRS transmit beam pattern (step 500), as describedabove. In some embodiments, the TP 22 transmits information related to aDRS transmission configuration for one or more cells to the wirelessdevice 20, as described above (step 502). The wireless device 20 obtainsthe information related to the DRS transmission configuration (step 504)and, based on this information, performs one or more measurements on theDRS signal(s) transmitted by the TP 22 (step 506). The wireless device20 then uses the measurement(s), as described above (step 508).

Although the described solutions may be implemented in any appropriatetype of telecommunication system supporting any suitable communicationstandards and using any suitable components, particular embodiments ofthe described solutions may be implemented in an LTE network 24, such asthat illustrated in FIG. 12 . As shown in FIG. 12 , the example LTEnetwork 24 may include one or more instances of wireless devices 20,which are also referred to herein as wireless communication devices 20,(e.g., conventional UEs or MTC/M2M UEs) and one or more TPs 22 (e.g.,radio access nodes such as, e.g., the macro node 12 and/or the RRHs 16of FIG. 6 ) capable of communicating with the wireless devices 20 alongwith any additional elements suitable to support communication betweenthe wireless devices 20 or between a wireless device 20 and anothercommunication device (such as a landline telephone). Although theillustrated wireless devices 20 may represent communication devices thatinclude any suitable combination of hardware and/or software, thesewireless devices 20 may, in particular embodiments, represent devicessuch as the example wireless device 20 illustrated in greater detail byFIGS. 13 and 14 . Similarly, although the illustrated TPs 22 mayrepresent network nodes that include any suitable combination ofhardware and/or software, these nodes may, in particular embodiments,represent devices such as the example TP 22 illustrated in greaterdetail by FIGS. 15 through 17 .

As shown in FIG. 13 , the example wireless device 20 includes aprocessor 26 (e.g., processing circuitry such as, for example, one ormore Central Processing Units (CPUs), one or more Application SpecificIntegrated Circuits (ASICs), one or more Field Programmable Gate Arrays(FPGAs), and/or the like), memory 28, a transceiver(s) 30, and anantenna(s) 32. In particular embodiments, some or all of thefunctionality described above as being provided by UEs, MTC or M2Mdevices, and/or any other types of wireless devices 20 may be providedby the processor 26 executing instructions stored on a computer-readablemedium, such as the memory 28 shown in FIG. 13 . Alternative embodimentsof the wireless device 20 may include additional components beyond thoseshown in FIG. 13 that may be responsible for providing certain aspectsof the device's functionality, including any of the functionalitydescribed above and/or any functionality necessary to support thesolution described above.

FIG. 14 illustrates the wireless device 20 according to some otherembodiments of the present disclosure. As illustrated, the wirelessdevice 20 includes an optional capability transmission module 34, aninformation obtaining module 36, a measurement module 38, and a usemodule 40, each of which is implemented in software. The optionalcapability transmission module 34 operates to transmit capabilityinformation to, e.g., a network node, as described above. Theinformation obtaining module 36 operates to obtain information relatedto DRS transmission configuration, as described above. The measurementmodule 38 operates to perform measurement(s) in accordance with theobtained information, as described above. The use module 40 operates touse the measurement(s) to perform one or more radio operation tasks, asdescribed above.

As shown in FIG. 15 , the example TP 22 (e.g., a radio access node suchas the macro node 12 or an RRH 16) includes a processor 42 (e.g.,processing circuitry such as, for example, one or more CPUs, one or moreASICs, one or more FPGAs, and/or the like), memory 44, a transceiver(s)46, and an antenna(s) 48. As discussed above, in the embodimentsdescribed herein, the antenna(s) 48 include multiple antennas. Inaddition, the TP 22 includes a network interface 50 that enablescommunication with other network nodes (e.g., nodes in the corenetwork). In particular embodiments, some or all of the functionalitydescribed above as being provided by a network node may be provided bythe processor 42 executing instructions stored on a computer-readablemedium, such as the memory 44 shown in FIG. 15 . Alternative embodimentsof the TP 22 may include additional components responsible for providingadditional functionality, including any of the functionality identifiedabove and/or any functionality necessary to support the solutiondescribed above.

FIG. 16 is a schematic block diagram that illustrates a virtualizedembodiment of the TP 22 (e.g., a virtualized embodiment of a networknode such as a radio access node) according to some embodiments of thepresent disclosure. As used herein, a “virtualized” network node is anetwork node in which at least a portion of the functionality of thenetwork node is implemented as a virtual component (e.g., via a virtualmachine(s) executing on a physical processing node(s) in a network(s)).As illustrated, the TP 22 includes the processor 42, the memory 44, andthe network interface 50 as well as the transceiver 46 coupled to theantennas 48, as described above. In this example, the processor 42, thememory 44, and the network interface 50 are embodied in a baseband unit52 that is connected to the transceiver 46 via, for example, an opticalcable or the like. The baseband unit 52 is connected to one or moreprocessing nodes 54 coupled to or included as part of a network(s) 56via the network interface 50. Each processing node 54 includes one ormore processors 58 (e.g., CPUs, ASICs, FPGAs, and/or the like), memory60, and a network interface 62.

In this example, functions 64 of the TP 22 described herein areimplemented at the one or more processing nodes 54 or distributed acrossthe baseband unit 52 and the one or more processing nodes 54 in anydesired manner. In some particular embodiments, some or all of thefunctions 64 of the TP 22 described herein are implemented as virtualcomponents executed by one or more virtual machines implemented in avirtual environment(s) hosted by the processing node(s) 54. As will beappreciated by one of ordinary skill in the art, additional signaling orcommunication between the processing node(s) 54 and the baseband unit 52is used in order to carry out at least some of the desired functions.Notably, in some embodiments, the baseband unit 52 may not be included,in which case the transceiver 46 communicates directly with theprocessing node(s) 54 via an appropriate network interface(s).

FIG. 17 illustrates the TP 22 according to some other embodiments of thepresent disclosure. As illustrated, the TP 22 includes an optionalcapability reception module 66, an optional information transmissionmodule 68, a DRS transmission module 70, and an optional measurementreception and use module 72, each of which is implemented in software.The capability reception module 66 operates to, in some embodiments,receive capability information from the wireless devices 20. Theinformation transmission module 68 operates to transmit informationrelated to DRS transmission configuration for one or more cells to thewireless device(s) 20, as described above. The DRS transmission module70 operates to transmit DRS signals as described above. The measurementreception and use module 72 operates to receive and use measurementsfrom the wireless devices 20, as described above.

Embodiments of the present disclosure can be implemented by hardware,software, or a combination of hardware and software. Embodiments can beimplemented as computer programs tangibly embodied on computer programproducts, hardware memory, or other structures. Embodiments may beimplemented on hardware modules, software modules, or a combination ofhardware and software modules.

The Following Acronyms are used throughout this Disclosure.

-   -   2D Two-Dimensional    -   3GPP Third Generation Partnership Project    -   AAS Active Antenna System    -   AoA Angle of Arrival    -   AP Access Point    -   ASIC Application Specific Integrated Circuit    -   BTS Base Transceiver Station    -   CA Carrier Aggregation    -   CDMA Code Division Multiple Access    -   CGI Cell Global Identity    -   CPU Central Processing Unit    -   CQI Channel Quality Indication    -   CRS Common Reference Signal    -   CSI Channel State Information    -   CSI-RS Channel State Information Reference Signal    -   D2D Device-to-Device    -   DC Dual Connectivity    -   DMTC Discovery Measurement Timing Configuration    -   DRS Discovery Reference Signal    -   DwPTS Downlink Part of the Special Subframe    -   EDGE Enhanced Data Rates for Global System for Mobile        Communications Evolution    -   eNB Enhanced or Evolved Node B    -   E-SMLC Evolved Serving Mobile Location Center    -   FDD Frequency Division Duplexing    -   FPGA Field Programmable Gate Array    -   GERAN Global System for Mobile Communications Enhanced Data        Rates for Global System for Mobile Communications Evolution        Radio Access Network    -   GNSS Global Navigation Satellite System    -   GPS Global Positioning System    -   GSM Global System for Mobile Communications    -   HSPA High Speed Packet Access    -   ID Identity    -   LEE Laptop Embedded Equipment    -   LME Laptop Mounted Equipment    -   LTE Long Term Evolution    -   M2M Machine-to-Machine    -   MAC Media Access Control    -   MDT Minimization of Drive Test    -   MIMO Multiple Input Multiple Output    -   MME Mobility Management Entity    -   ms Millisecond    -   MSC Mobile Switching Center    -   MSR Multi-Standard Radio    -   MTC Machine Type Communication    -   NZP Non-Zero Power    -   O&M Operations and Management    -   OFDM Orthogonal Frequency Division Multiplexing    -   OSS Operations Support System    -   PBCH Physical Broadcast Channel    -   PCC Primary Component Carrier    -   PCell Primary Cell    -   PCI Physical Cell Identity    -   PDA Personal Digital Assistant    -   PRB Physical Resource Block    -   ProSe Proximity Service    -   PRS Positioning Reference Signal    -   PSCC Primary Secondary Component Carrier    -   PSS Primary Synchronization Signal    -   RAT Radio Access Technology    -   RB Resource Block    -   RE Resource Element    -   Rel-12 Release 12    -   RF Radio Frequency    -   RRC Radio Resource Control    -   RRH Remote Radio Head    -   RRM Radio Resource Management    -   RRU Remote Radio Unit    -   RSRP Reference Signal Received Power    -   RSRQ Reference Signal Received Quality    -   RSSI Received Signal Strength Indication    -   SCC Secondary Component Carrier    -   SCell Secondary Cell    -   SFN System Frame Number    -   SINR Signal to Interference plus Noise Ratio    -   SON Self-Organizing Node    -   SSS Secondary Synchronization Signal    -   TDD Time Division Duplexing    -   TP Transmission Point    -   TS Technical Specification    -   TTI Transmit Time Interval    -   UE User Equipment    -   USB Universal Serial Bus    -   VCID Virtual or Configurable Cell Identity    -   WCDMA Wideband Code Division Multiple Access    -   WLAN Wireless Local Area Network    -   ZP Zero Power

Those skilled in the art will recognize improvements and modificationsto the embodiments of the present disclosure. All such improvements andmodifications are considered within the scope of the concepts disclosedherein and the claims that follow.

The invention claimed is:
 1. A method of operation of a transmissionpoint in a cellular communications network, comprising: transmitting,from the transmission point, a same one or more Discovery ReferenceSignal, DRS, signals using at least two different transmit beams in atleast two different time resources of two different subframes, eachtransmit beam being characterized by a direction in which it istransmitted.
 2. The method of claim 1 wherein transmitting the same oneor more DRS signals using the at least two different transmit beams inthe at least two different time resources comprises: transmitting theone or more DRS signals using a first transmit beam, but not a secondtransmit beam, in a first time resource; and transmitting the one ormore DRS signals using the second transmit beam, but not the firsttransmit beam, in a second time resource, the second transmit beam beingdifferent than the first transmit beam and the second time resourcebeing different than the first time resource.
 3. The method of claim 1wherein the one or more DRS signals comprise a Channel State InformationReference Signal, CSI-RS.
 4. The method of claim 3 wherein the one ormore DRS signals comprise: a Primary Synchronization Signal, PSS, for aPhysical Cell Identity, PCI; a Secondary Synchronization Signal, SSS,for the same PCI; and a Common Reference Signal, CRS, for the same PCI.5. The method of claim 1 wherein the at least two different timeresources are at least two different DRS occasions, and transmitting thesame one or more DRS signals using the at least two different transmitbeams in the at least two different time resources comprisestransmitting the same one or more DRS signals using the at least twodifferent transmit beams in the at least two different DRS occasions. 6.The method of claim 1 wherein the at least two different time resourcesare at least two time resources within a same DRS occasion, andtransmitting the same one or more DRS signals using the at least twodifferent transmit beams in the at least two different time resourcescomprises transmitting the same one or more DRS signals using the atleast two different transmit beams in the at least two different timeresources within the same DRS occasion.
 7. The method of claim 1 whereintransmitting the same one or more DRS signals using the at least twodifferent transmit beams in the at least two different time resourcescomprises transmitting the same one or more DRS signals according to aDRS transmit beam pattern that defines the at least two differenttransmit beams in the at least two different time resources in which theone or more DRS signals are to be transmitted.
 8. The method of claim 7wherein the DRS transmit beam pattern is a symmetric DRS transmit beampattern.
 9. The method of claim 7 wherein the DRS transmit beam patternis an asymmetric DRS transmit beam pattern.
 10. The method of claim 7wherein the DRS transmit beam pattern is an aperiodic DRS transmit beampattern.
 11. The method of claim 1 wherein transmitting the same one ormore DRS signals using the at least two different transmit beams in theat least two different time resources comprises: deciding that the oneor more DRS signals are to be transmitted using a DRS transmit beampattern; deciding which DRS transmit beam pattern is to be used fortransmission of the one or more DRS signals; and transmitting the sameone or more DRS signals using the at least two different transmit beamsin the at least two different time resources in accordance with the DRStransmit beam pattern.
 12. The method of claim 11 wherein deciding thatthe one or more DRS signals are to be transmitted using a DRS transmitbeam pattern comprises deciding that the one or more DRS signals are tobe transmitted using a DRS transmit beam pattern based on one or morecriteria selected from a group consisting of: a criterion that a requestto use a DRS transmit beam pattern is received from another networknode; a criterion that a DRS transmit beam pattern is to be used whenbeamforming is used or is expected to be used by the transmission point;a criterion that a DRS transmit beam pattern is to be used when a numberof transmit beams being used or expected to be used by the transmissionpoint is greater than a predefined threshold; a criterion that a DRStransmit beam pattern is to be used when there is a large number ofradio nodes in a coverage area of the transmission point; a criterionthat a DRS transmit beam pattern is to be used when there is a limitednumber of different DRS resources available; a criterion that a DRStransmit beam pattern is to be used for a particular deploymentscenario; a criterion that a DRS transmit beam pattern is to be usedwhen system load is greater than a predefined threshold; a criterionbased on measurement performance; and a criterion based on one or moreDRS transmission parameters.
 13. The method of claim 1 whereintransmitting the same one or more DRS signals using the at least twodifferent transmit beams in the at least two different time resourcescomprises transmitting the same one or more DRS signals according to aDRS transmit beam pattern that defines the at least two differenttransmit beams in the at least two different time resources in which theone or more DRS signals are to be transmitted, and the method furthercomprises: providing information to a wireless device related totransmission of the one or more DRS signals in accordance with the DRStransmit beam pattern.
 14. The method of claim 13 wherein theinformation comprises an indication that the transmission point is or isexpected to transmit DRS signals according to a DRS transmit beampattern.
 15. The method of claim 13 wherein the information comprises anindication that the transmission point is or is expected to transmit theone or more DRS signals according to the DRS transmit beam pattern. 16.The method of claim 13 wherein the information comprises informationrelated to transmission of DRS signals in accordance with DRS transmitbeam patterns in multiple cells.
 17. The method of claim 1 whereintransmitting the same one or more DRS signals using the at least twodifferent transmit beams in the at least two different time resourcescomprises transmitting the same one or more DRS signals according to aDRS transmit beam pattern that defines the at least two differenttransmit beams in the at least two different time resources in which theone or more DRS signals are to be transmitted, and the method furthercomprises: providing information to another network node related totransmission of the one or more DRS signals, by the transmission point,in accordance with the DRS transmit beam pattern.
 18. The method ofclaim 1 further comprising: receiving one or more measurements from awireless device based on the one or more DRS signals transmitted usingthe at least two different transmit beams in the at least two differenttime resources; and correlating each measurement of the one or moremeasurements to a respective one of the at least two different transmitbeams.
 19. The method of claim 18 wherein: transmitting the same one ormore DRS signals using the at least two different transmit beams in theat least two different time resources comprises transmitting the sameone or more DRS signals according to a DRS transmit beam pattern thatdefines the at least two different transmit beams in the at least twodifferent time resources in which the one or more DRS signals are to betransmitted; and correlating each measurement of the one or moremeasurements to a respective one of the at least two different transmitbeams comprises correlating each measurement of the one or moremeasurements to the respective one of the at least two differenttransmit beams based on a known time resource in which the measurementwas obtained and the DRS transmit beam pattern.